1 | /* |
2 | * I2C multiplexer driver for PCA9541 bus master selector |
3 | * |
4 | * Copyright (c) 2010 Ericsson AB. |
5 | * |
6 | * Author: Guenter Roeck <linux@roeck-us.net> |
7 | * |
8 | * Derived from: |
9 | * pca954x.c |
10 | * |
11 | * Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it> |
12 | * Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it> |
13 | * |
14 | * This file is licensed under the terms of the GNU General Public |
15 | * License version 2. This program is licensed "as is" without any |
16 | * warranty of any kind, whether express or implied. |
17 | */ |
18 | |
19 | #include <linux/bitops.h> |
20 | #include <linux/delay.h> |
21 | #include <linux/device.h> |
22 | #include <linux/i2c.h> |
23 | #include <linux/i2c-mux.h> |
24 | #include <linux/jiffies.h> |
25 | #include <linux/module.h> |
26 | #include <linux/slab.h> |
27 | |
28 | /* |
29 | * The PCA9541 is a bus master selector. It supports two I2C masters connected |
30 | * to a single slave bus. |
31 | * |
32 | * Before each bus transaction, a master has to acquire bus ownership. After the |
33 | * transaction is complete, bus ownership has to be released. This fits well |
34 | * into the I2C multiplexer framework, which provides select and release |
35 | * functions for this purpose. For this reason, this driver is modeled as |
36 | * single-channel I2C bus multiplexer. |
37 | * |
38 | * This driver assumes that the two bus masters are controlled by two different |
39 | * hosts. If a single host controls both masters, platform code has to ensure |
40 | * that only one of the masters is instantiated at any given time. |
41 | */ |
42 | |
43 | #define PCA9541_CONTROL 0x01 |
44 | #define PCA9541_ISTAT 0x02 |
45 | |
46 | #define PCA9541_CTL_MYBUS BIT(0) |
47 | #define PCA9541_CTL_NMYBUS BIT(1) |
48 | #define PCA9541_CTL_BUSON BIT(2) |
49 | #define PCA9541_CTL_NBUSON BIT(3) |
50 | #define PCA9541_CTL_BUSINIT BIT(4) |
51 | #define PCA9541_CTL_TESTON BIT(6) |
52 | #define PCA9541_CTL_NTESTON BIT(7) |
53 | |
54 | #define PCA9541_ISTAT_INTIN BIT(0) |
55 | #define PCA9541_ISTAT_BUSINIT BIT(1) |
56 | #define PCA9541_ISTAT_BUSOK BIT(2) |
57 | #define PCA9541_ISTAT_BUSLOST BIT(3) |
58 | #define PCA9541_ISTAT_MYTEST BIT(6) |
59 | #define PCA9541_ISTAT_NMYTEST BIT(7) |
60 | |
61 | #define BUSON (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON) |
62 | #define MYBUS (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS) |
63 | #define mybus(x) (!((x) & MYBUS) || ((x) & MYBUS) == MYBUS) |
64 | #define busoff(x) (!((x) & BUSON) || ((x) & BUSON) == BUSON) |
65 | |
66 | /* arbitration timeouts, in jiffies */ |
67 | #define ARB_TIMEOUT (HZ / 8) /* 125 ms until forcing bus ownership */ |
68 | #define ARB2_TIMEOUT (HZ / 4) /* 250 ms until acquisition failure */ |
69 | |
70 | /* arbitration retry delays, in us */ |
71 | #define SELECT_DELAY_SHORT 50 |
72 | #define SELECT_DELAY_LONG 1000 |
73 | |
74 | struct pca9541 { |
75 | struct i2c_client *client; |
76 | unsigned long select_timeout; |
77 | unsigned long arb_timeout; |
78 | }; |
79 | |
80 | static const struct i2c_device_id pca9541_id[] = { |
81 | {"pca9541" , 0}, |
82 | {} |
83 | }; |
84 | |
85 | MODULE_DEVICE_TABLE(i2c, pca9541_id); |
86 | |
87 | #ifdef CONFIG_OF |
88 | static const struct of_device_id pca9541_of_match[] = { |
89 | { .compatible = "nxp,pca9541" }, |
90 | {} |
91 | }; |
92 | MODULE_DEVICE_TABLE(of, pca9541_of_match); |
93 | #endif |
94 | |
95 | /* |
96 | * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer() |
97 | * as they will try to lock the adapter a second time. |
98 | */ |
99 | static int pca9541_reg_write(struct i2c_client *client, u8 command, u8 val) |
100 | { |
101 | struct i2c_adapter *adap = client->adapter; |
102 | union i2c_smbus_data data = { .byte = val }; |
103 | |
104 | return __i2c_smbus_xfer(adapter: adap, addr: client->addr, flags: client->flags, |
105 | I2C_SMBUS_WRITE, command, |
106 | I2C_SMBUS_BYTE_DATA, data: &data); |
107 | } |
108 | |
109 | /* |
110 | * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer() |
111 | * as they will try to lock adapter a second time. |
112 | */ |
113 | static int pca9541_reg_read(struct i2c_client *client, u8 command) |
114 | { |
115 | struct i2c_adapter *adap = client->adapter; |
116 | union i2c_smbus_data data; |
117 | int ret; |
118 | |
119 | ret = __i2c_smbus_xfer(adapter: adap, addr: client->addr, flags: client->flags, |
120 | I2C_SMBUS_READ, command, |
121 | I2C_SMBUS_BYTE_DATA, data: &data); |
122 | |
123 | return ret ?: data.byte; |
124 | } |
125 | |
126 | /* |
127 | * Arbitration management functions |
128 | */ |
129 | |
130 | /* Release bus. Also reset NTESTON and BUSINIT if it was set. */ |
131 | static void pca9541_release_bus(struct i2c_client *client) |
132 | { |
133 | int reg; |
134 | |
135 | reg = pca9541_reg_read(client, PCA9541_CONTROL); |
136 | if (reg >= 0 && !busoff(reg) && mybus(reg)) |
137 | pca9541_reg_write(client, PCA9541_CONTROL, |
138 | val: (reg & PCA9541_CTL_NBUSON) >> 1); |
139 | } |
140 | |
141 | /* |
142 | * Arbitration is defined as a two-step process. A bus master can only activate |
143 | * the slave bus if it owns it; otherwise it has to request ownership first. |
144 | * This multi-step process ensures that access contention is resolved |
145 | * gracefully. |
146 | * |
147 | * Bus Ownership Other master Action |
148 | * state requested access |
149 | * ---------------------------------------------------- |
150 | * off - yes wait for arbitration timeout or |
151 | * for other master to drop request |
152 | * off no no take ownership |
153 | * off yes no turn on bus |
154 | * on yes - done |
155 | * on no - wait for arbitration timeout or |
156 | * for other master to release bus |
157 | * |
158 | * The main contention point occurs if the slave bus is off and both masters |
159 | * request ownership at the same time. In this case, one master will turn on |
160 | * the slave bus, believing that it owns it. The other master will request |
161 | * bus ownership. Result is that the bus is turned on, and master which did |
162 | * _not_ own the slave bus before ends up owning it. |
163 | */ |
164 | |
165 | /* Control commands per PCA9541 datasheet */ |
166 | static const u8 pca9541_control[16] = { |
167 | 4, 0, 1, 5, 4, 4, 5, 5, 0, 0, 1, 1, 0, 4, 5, 1 |
168 | }; |
169 | |
170 | /* |
171 | * Channel arbitration |
172 | * |
173 | * Return values: |
174 | * <0: error |
175 | * 0 : bus not acquired |
176 | * 1 : bus acquired |
177 | */ |
178 | static int pca9541_arbitrate(struct i2c_client *client) |
179 | { |
180 | struct i2c_mux_core *muxc = i2c_get_clientdata(client); |
181 | struct pca9541 *data = i2c_mux_priv(muxc); |
182 | int reg; |
183 | |
184 | reg = pca9541_reg_read(client, PCA9541_CONTROL); |
185 | if (reg < 0) |
186 | return reg; |
187 | |
188 | if (busoff(reg)) { |
189 | int istat; |
190 | /* |
191 | * Bus is off. Request ownership or turn it on unless |
192 | * other master requested ownership. |
193 | */ |
194 | istat = pca9541_reg_read(client, PCA9541_ISTAT); |
195 | if (!(istat & PCA9541_ISTAT_NMYTEST) |
196 | || time_is_before_eq_jiffies(data->arb_timeout)) { |
197 | /* |
198 | * Other master did not request ownership, |
199 | * or arbitration timeout expired. Take the bus. |
200 | */ |
201 | pca9541_reg_write(client, |
202 | PCA9541_CONTROL, |
203 | val: pca9541_control[reg & 0x0f] |
204 | | PCA9541_CTL_NTESTON); |
205 | data->select_timeout = SELECT_DELAY_SHORT; |
206 | } else { |
207 | /* |
208 | * Other master requested ownership. |
209 | * Set extra long timeout to give it time to acquire it. |
210 | */ |
211 | data->select_timeout = SELECT_DELAY_LONG * 2; |
212 | } |
213 | } else if (mybus(reg)) { |
214 | /* |
215 | * Bus is on, and we own it. We are done with acquisition. |
216 | * Reset NTESTON and BUSINIT, then return success. |
217 | */ |
218 | if (reg & (PCA9541_CTL_NTESTON | PCA9541_CTL_BUSINIT)) |
219 | pca9541_reg_write(client, |
220 | PCA9541_CONTROL, |
221 | val: reg & ~(PCA9541_CTL_NTESTON |
222 | | PCA9541_CTL_BUSINIT)); |
223 | return 1; |
224 | } else { |
225 | /* |
226 | * Other master owns the bus. |
227 | * If arbitration timeout has expired, force ownership. |
228 | * Otherwise request it. |
229 | */ |
230 | data->select_timeout = SELECT_DELAY_LONG; |
231 | if (time_is_before_eq_jiffies(data->arb_timeout)) { |
232 | /* Time is up, take the bus and reset it. */ |
233 | pca9541_reg_write(client, |
234 | PCA9541_CONTROL, |
235 | val: pca9541_control[reg & 0x0f] |
236 | | PCA9541_CTL_BUSINIT |
237 | | PCA9541_CTL_NTESTON); |
238 | } else { |
239 | /* Request bus ownership if needed */ |
240 | if (!(reg & PCA9541_CTL_NTESTON)) |
241 | pca9541_reg_write(client, |
242 | PCA9541_CONTROL, |
243 | val: reg | PCA9541_CTL_NTESTON); |
244 | } |
245 | } |
246 | return 0; |
247 | } |
248 | |
249 | static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan) |
250 | { |
251 | struct pca9541 *data = i2c_mux_priv(muxc); |
252 | struct i2c_client *client = data->client; |
253 | int ret; |
254 | unsigned long timeout = jiffies + ARB2_TIMEOUT; |
255 | /* give up after this time */ |
256 | |
257 | data->arb_timeout = jiffies + ARB_TIMEOUT; |
258 | /* force bus ownership after this time */ |
259 | |
260 | do { |
261 | ret = pca9541_arbitrate(client); |
262 | if (ret) |
263 | return ret < 0 ? ret : 0; |
264 | |
265 | if (data->select_timeout == SELECT_DELAY_SHORT) |
266 | udelay(data->select_timeout); |
267 | else |
268 | msleep(msecs: data->select_timeout / 1000); |
269 | } while (time_is_after_eq_jiffies(timeout)); |
270 | |
271 | return -ETIMEDOUT; |
272 | } |
273 | |
274 | static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan) |
275 | { |
276 | struct pca9541 *data = i2c_mux_priv(muxc); |
277 | struct i2c_client *client = data->client; |
278 | |
279 | pca9541_release_bus(client); |
280 | return 0; |
281 | } |
282 | |
283 | /* |
284 | * I2C init/probing/exit functions |
285 | */ |
286 | static int pca9541_probe(struct i2c_client *client) |
287 | { |
288 | struct i2c_adapter *adap = client->adapter; |
289 | struct i2c_mux_core *muxc; |
290 | struct pca9541 *data; |
291 | int ret; |
292 | |
293 | if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA)) |
294 | return -ENODEV; |
295 | |
296 | /* |
297 | * I2C accesses are unprotected here. |
298 | * We have to lock the I2C segment before releasing the bus. |
299 | */ |
300 | i2c_lock_bus(adapter: adap, I2C_LOCK_SEGMENT); |
301 | pca9541_release_bus(client); |
302 | i2c_unlock_bus(adapter: adap, I2C_LOCK_SEGMENT); |
303 | |
304 | /* Create mux adapter */ |
305 | |
306 | muxc = i2c_mux_alloc(parent: adap, dev: &client->dev, max_adapters: 1, sizeof_priv: sizeof(*data), |
307 | I2C_MUX_ARBITRATOR, |
308 | select: pca9541_select_chan, deselect: pca9541_release_chan); |
309 | if (!muxc) |
310 | return -ENOMEM; |
311 | |
312 | data = i2c_mux_priv(muxc); |
313 | data->client = client; |
314 | |
315 | i2c_set_clientdata(client, data: muxc); |
316 | |
317 | ret = i2c_mux_add_adapter(muxc, force_nr: 0, chan_id: 0, class: 0); |
318 | if (ret) |
319 | return ret; |
320 | |
321 | dev_info(&client->dev, "registered master selector for I2C %s\n" , |
322 | client->name); |
323 | |
324 | return 0; |
325 | } |
326 | |
327 | static void pca9541_remove(struct i2c_client *client) |
328 | { |
329 | struct i2c_mux_core *muxc = i2c_get_clientdata(client); |
330 | |
331 | i2c_mux_del_adapters(muxc); |
332 | } |
333 | |
334 | static struct i2c_driver pca9541_driver = { |
335 | .driver = { |
336 | .name = "pca9541" , |
337 | .of_match_table = of_match_ptr(pca9541_of_match), |
338 | }, |
339 | .probe = pca9541_probe, |
340 | .remove = pca9541_remove, |
341 | .id_table = pca9541_id, |
342 | }; |
343 | |
344 | module_i2c_driver(pca9541_driver); |
345 | |
346 | MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>" ); |
347 | MODULE_DESCRIPTION("PCA9541 I2C master selector driver" ); |
348 | MODULE_LICENSE("GPL v2" ); |
349 | |